Martin von Zweigbergk <martinvonz@google.com> [Fri, 03 Dec 2021 22:45:35 -0800] rev 48432
filemerge: inline `_filemerge()` into `filemerge()`
The caller is now trivial, so the indirection is pointless.
Differential Revision: https://phab.mercurial-scm.org/D11860